"The legal group wanted me to do a validation study β me, as an unbiased independent researcher β and whatever the outcome was, I was to do a comprehensive study and provide them with the results," Jo explained to Wareable.

The result of which, as you may have read earlier this week, concluded that Fitbit's heart rate accuracy is, on average, 20 beats per minute inaccurate during moderate to high-intensity exercise.

"This inaccuracy that we've seen can definitely pose a danger to not only the clinical population, but those population of individuals who may not know that they have any cardiac related conditions," said Jo. "It can definitely put them at risk."

However, Fitbit has quickly moved to counter the results of the study, and contacted us to state: "What the plaintiffs' attorneys call a 'study' is biased, baseless, and nothing more than an attempt to extract a payout from Fitbit. It lacks scientific rigor and is the product of flawed methodology. It was paid for by plaintiffs' lawyers who are suing Fitbit, and was conducted with a consumer-grade electrocardiogram β not a true clinical device, as implied by the plaintiffs' lawyers. Furthermore, there is no evidence the device used in the purported 'study' was tested for accuracy."

Firm words indeed, but words that didn't take Dr. Jo by surprise.

"It's expected obviously," he responded. "They're not going to say, 'Oh great job Dr. Jo'. If the result of an independent study is not in the favour of the product, obviously the manufacturer will come up with a generic rebuttal β and one of the most generic ones is to say it's flawed methodology."

Fitbit on the ropes

"Mudslinging in a litigation contest is not that unfamiliar but I was a little bit insulted on their behalf to the depths that Fitbit has stooped to call out independent researchers who have done many validation studies," Kevin Budner, one of the attorneys working on the case against Fitbit, told us.

"There is absolutely zero incentive for an academic to sully their reputation with a biased report. If anybody is misrepresenting the facts and the reality of the world to gain a profit, then it's Fitbit. They very aggressively market a heart rate feature, knowing it's a big selling point, saying 'every beat counts' and 'know your heart'," he added.

With regards to the Zephyr Technology BioHarness, the device used in the study to compare the Fitbits to, Jo himself had this to say: "The device has been validated twice to the traditional 12-lead ECG and also a 3-lead ECG for heart rate measurement. It's FDA approved, so for them to say it's not a clinical grade device β well, I don't even know what that means."

A Fitbit spokesperson also highlighted an additional study, one by Consumer Reports, that gave the Surge and HR an 'excellent' rating. However, that study is useless according to Dr. Jo, as there were only two individuals tested.

"If they're talking about flawed methodology, this one had the most minimal amount of scientific rigor you could possibly have," argued Jo. "It's crude, not sophisticated and has minimal data. They say they did statistical analysis β you can't do statistical analysis with just two data points. And this is their go-to reference?"

Jo told us that his study involved 43 subjects simultaneously wearing a Surge and Charge HR on each wrist, resulting in over 120,000 data points in controlled conditions.

Surge and Charge HR inaccuracies

Jo also explained that the inaccuracies he reported were not consistent and, more worryingly, he also noted differences between Fitbit's own devices, while the individual user was wearing both at the same time.

"If the difference was systematic, that would be one thing β say always underestimating by 20 beats all the time compared to the ECG," he said. "But those differences were sporadic. It was ambiguous and all over the place.

"Another separate analysis that we did was comparing the data from the Charge HR versus the Fitbit Surge," he added. "They are purported to have the same optical heart rate sensor. So you'd think the results for an individual would be the same for a given time point but we saw inconsistencies. It was off. From a statistical standpoint it was significantly off."

Fitbit disputes the report and has always maintained that its devices are consumer products and not medical devices. However, the attorney Budner has issues with that distancing.

"They're bandying about this term 'medical device' like it's the be-all and end-all," he told us. "But it's kind of a red-herring. The issue is they advertise it and sell it, at a premium, to do something β monitor your heart rate during exercise.

"It doesn't matter if it's a medical device or not a medical device, they tell the consumers it will do one thing, consumers buy it and it turns out that it doesn't do that thing. That's classic consumer fraud and I think that's what we're dealing with here.

"We're not saying that this is supposed to be an ECG; it's a consumer device. But there are a lot of consumer devices out there that actually do provide close and meaningful heart data to consumers β and these Fitbit devices simply don't."

Fitbit leading the way

Fitbit has told us that its research team rigorously researched and developed PurePulse technology for three years before introducing it "and continues to conduct extensive internal studies to test the features of our products."

The company was also keen to express us that the Fitbit Charge HR is the top selling fitness tracker on the market, and is "embraced by millions of consumers around the globe."

We at Wareable actually rate the Fitbit Blaze, featuring PurePulse technology, as our best all-round fitness tracker. However, as we lamented the sporadic bpm recordings of both the Surge and the Charge HR in their reviews in 2015, we also had big concerns about the Blaze's performance during exercise.

"As we upped the pace, things fell apart," wrote executive editor James Stables in his review. "As our heart rate rose up from 150bpm to 165bpm, the Fitbit remained static, locked to 150bpm. As we started to sprint the chest strap reported 170β180bpm, yet still the Fitbit stayed at 150.

"Later in the run it came back to the chest strap at around 165 as we started to cool down. It's a disaster zoneβ¦ The Blaze's tracking can't handle high intensity, and what's more, it suffers from a dreadful lag time, making its suitability for hardcore sessions non-existent."

Fitbit may have the fitness tracker market sewn up but it seems it has a long way to go before it can truly boast about its HRM credentials.

1 comment

Yacker·04-Jun-2019 12:09 am

As a conditioned runner I monitor my pulse rate will working out at my gym on high end treadmills. Depending on my workout, my pulse rate on various treadmills stays between 115 to 125bpm. My Fitbit Charger 2 repeatedly shows 155 - 165bpm. Yikes